


Kid Yeager

by Eraishu



Series: Eren Experimentation Series [1]
Category: Shingeki no Kyojin | Attack on Titan
Genre: Child Eren Yeager, Cute Eren Yeager, Ereri/Riren if you squint, Everyone Is Alive, Special Operations Squad | Squad Levi Lives, Teen and up bcuz of Levi's bad mouth, Well not everyone
Language: English
Status: Completed
Published: 2020-10-24
Updated: 2020-10-24
Packaged: 2021-03-08 18:21:58
Rating: Teen And Up Audiences
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 6
Words: 4,092
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/27171017
Author URL: https://archiveofourown.org/users/Eraishu/pseuds/Eraishu
Summary: Hange loves to experiment on Eren.One day, Hange made a potion to shrink living beings to try and test on Eren. However, instead of just shrinking Eren, it actually changes him into the body of a five year-old. Both mentally and physically.This is what happens....
Relationships: Mikasa Ackerman & Armin Arlert & Eren Yeager
Series: Eren Experimentation Series [1]
Series URL: https://archiveofourown.org/series/2030389
Comments: 4
Kudos: 94
Collections: The Eren Experiment Series





	1. Where's Eren?

**Author's Note:**

> This is my very first fanfic so please be gentle...
> 
> Also, a bit of a disclaimer, I'm not very good at capturing a character's personality, so a this might be a b OOC....
> 
> Happy Reading!

It was a normal day inside of the Survey Corps headquarters..

"Uuuuugh..." The 104th squad were re-cleaning their sleeping quarters. "Why do we have to re-do our rooms?!.." Connie sighed.

"Because our cleaning was not up to Captain Levi's standards, apparently.." Answered Armin.

"How clean is Captain Levi's standards, Armin?" Historia questioned.

"Super-clean, I guess..."

"How clean is super clean??" This time, Sasha had asked.

"Uhh-"

"Hey, brat" The squad froze.

"Yes, Captain?" They saluted.

Levi nodded

"What did you need, Captain?" Armin asked.

"Where's Eren?" Captain Levi asked, followed by silence.

Now that they had thought about it, they hadn't seen Eren anywhere since that morning.

"Hey, Mikasa." Armin broke the silence.

"Hmm.." Mikasa looks up from her cleaning.

"Have you seen Eren at all since this morning?"

"..." Silence was Mikasa's answer.

"..?" Armin tilted his head to the side and hummed curiously, urging Mikasa to answer.

"..Yes.." Mikasa finally answers.

"Whe-"

"Care to tell, brat." Levi said, breaking of Armin's words.

Mikasa glared at the raven-haired man. "Why should I tell you?" 

"Damn brat. It wasn't a question, it was an order." Captain Levi answered.

"I saw them getting dragged by Majo-"

Before she could even finish, Captain Levi had already lifted himself off the wall he was leaning on and made his way to the mayor's office.

**End of Chapter One**.


	2. A.. Child?

**Summary for the Chapter:**

> Meeting the tiny Eren!

**Notes for the Chapter:**

> Ooh~
> 
> Part on and two on the same day! I hope you'll enjoy!
> 
> Happy Reading!

"Shitty Glasses." The door to Hange's office burst open, revealing a short raven-haired corporal.

"Ah, My little Ravioli! What brings you to my office, today?"

"Where's the brat." Levi asked.

Silence...

"Answer my question, Shitty Glasses." Levi said, voice brimming with annoyance.

"Uhhhh...."

"Dammit, Hange, I don't have all day. Where. Is. Eren." Levi repeated word by word.

"W-well, you se-"

"What is that?!" Levi points to something by Hange's legs.

"What is- Oh." Hange hesitated, spotting a child by her legs. "..This is-"

"Corpowal!" The kid spoke and made grabby-hands towards Levi, his eyes almost shining.

"Wait- is that.." The Corporal started.

"It's Eren!" Hange finished, grabbing Eren and holding him closely.

"Waah!~" Eren giggled.

Levi glared at Hange, almost at a loss of words. "What did you do to him, Shit-brain."

"Well, you see...."

> **Five minutes ago.**

_"Excuse me, Major Hange?" Eren opened the door to Hange's lab._

_"Ah! Eren!" The Major jumped from their seat and ran towards the titan shifter._

_Hange hugs him. "Major! Y-your ch-choking me." Hange looks down to see the boy losing some breath._

_"Op- sorry, Eren.." Hange releases him, letting him breath._

_"Never mind, Major. Now what did you need me for?" Eren tilts his head curiously, making Hange squeal at his cuteness._

_"Today, I created a serum to make the living beings I inject it on, to shrink." Hange started. "Think about it Eren wouldn't the titans be so much cut- I mean easier to fight if they were smaller"_

_"Uh-huh! But, Major, what did you need **me** for?" Eren questioned._

_"Well I needed something else to test it on, since my experimentation titans ran away." Hange stated and Eren fought the urge to say what actually happened to them._

_"Me?... Sure, I guess." Eren could never reject the chance to actually help humanity win against the titans._

_"Good. Here, drink this." Hange hands them the serum._

> **Back to the present.**

"-and that's what happened.." Hange finished.

"Well, what the fuck are we supposed to do with this." Levi motions to the small child sleeping on Hange's desk. Eren had fallen asleep sometime while Hange was retelling the story.

"I guess I'll try to fix him up somehow. But-" Hange pauses, turns around and picks Eren up, waking the poor fella. "Do we have to he's so cute!!" Hange squeals, startling Eren.

"Yes, and give him to me, you're scaring him." Levi forcefully took Eren away from the mad scientist, secretly being very careful not to hurt the poor kid.

"That hurts, Levi!!" Hange pretends to be hurt, making Eren giggle.

"I don't care. Get to work." Levi left the scientist, leaving her no room to argue.

**End of Chapter Two.**

**Notes for the Chapter:**

> Thank you for reading.
> 
> Again, feel free to suggest other things Eren could turn into next!
> 
> Happy Day!


	3. That's Eren?!

**Summary for the Chapter:**

> The New Levi Squad finally get to meet Tiny Eren.

"Uh..." 

Eren was sitting in front of his friends in the Mess Hall. They all had wide eyes while trying to understand who the kid was.

"Awmin!" Eren runs up to Armin and hugs his shins.

"Armin you know the ki-"

"Eren." They all gasped at Mikasa's statement.

"Eren?!" Connie was flabbergasted.

Levi sighed and pulled out a stool to sit on. He had a bit of explaining to do.

With another sigh he opened his mouth to explain.

.

.

.

"So what you're saying is that this kid is the suicidal bastard himself?!!" Jean shouted.

"tch, noisy." Levi said but nodded as an answer to his question. 

"Is there a cure for it, Captain?" Armin asked this time.

"..So far, Shitty-glasses hasn't made one yet." Levi deadpanned. "They'll probably have to run some tests on the brat to make one too." he added.

At that, he saw Mikasa holding onto Eren's sleeping form tightly in the corner of his eye. 

' _Tch, the brat's asleep again_..'

Levi rubbed his temple, in-between his eyes and thought for a moment. After a few seconds he got up again and started walking to the hallway.

"Captain Levi, Where are you going?" Armin noticed him.

"I'm going to go tell our Commander-Eyebrows what happened, get his next order." Levi stated and left the 104th squad with Eren.

.

.

As soon as the captain left, they all gathered around where Mikasa was holding a sleeping Eren.

"Should we wake him up?" Jean asked which was answered by some collective _No!_ 's.

"Well what should we do then?" Connie had to ask this time. It was hard to take care of a kid when none of them had ever took care of one before. Armin and Mikasa knew Eren when they were children, but Eren is much younger than when they first met him.

"Maybe we should find him a good place to sleep." Historia recommended.

"That would be good, he's probably not very comfortable laying like that." Ymir helped, motioning to the way Eren was sleeping with his neck craned to the side.

Mikasa nodded and hummed as a sign of agreement. She picked Eren up and held him protectively against her chest.

"Where?" She asked.

Historia pointed to the table. "Spread your scarf out on the table so it's more comfortable." She added.

She took off her scarf and handed it to Armin who did as Historia told. When he was finished, he helped Mikasa put Eren on top of it. Eren fidgeted a bit but slowly got more comfortable on the makeshift bed. Once he was finally comfortable, the other members of the squad sat around the table Eren was sleeping on.

"Who knew Eren was this cute when he was a kid." Sasha said breaking the comfortable silence they were in, while admiring Eren's cute sleeping face.

"As much as I wouldn't like to admit it, I'd have to agree with you on that." Jean admitted.

Soon they fell into a comfortable silence again... but not for very long as Armin had remembered they had to continue their cleaning unless they wanted to make their captain mad again. They all left to continue their clean-ups with the exception of Mikasa and Historia to take care of Eren.

.

.

.

**End of Chapter Three**


	4. You'll be In-Charge.

**Summary for the Chapter:**

> Levi and his squad are now in-charge of taking care of Eren.

Levi had just reported the events of Eren turning into a 5-ish year old child to Erwin and was now on his way to tell both the new and old recruits of his squad.

When he opened the giant doors known as the doors to the Mess Hall, he was half expecting all of his squad to be there but was pleasantly surprised when he was informed that the others were still cleaning. 

He told Historia to call them over along with their superiors.

.

.

.

Once all the Members of the squad were there, Levi explained to his old squad on Eren's condition and also informed them about the order they were given.

"Squad Levi will be taking care of the brat, we will be taking turns to care for the him and there are no exceptions."

"Yes, Captain!" They all saluted.

"Yesh, Cawptain!" came a small voice after theirs.

They all turned towards Eren who had already woken up and stood beside Mikasa with his small fist held above his heart.

"So cute!" Petra squeled along with the other members. Eren was looking at them with curious eyes while tilting his head to the side like he always would when he was confused.

Levi watched as Eren tried to walk towards them but failed miserably when he tripped over the big shirt he usualy wore. Levi then got up and went towards him.

"Oi, brat." came Levi's voice, startling Eren. He tried to stand up as quickly as he could but tripped on his shirt again, only this time, he didn't fall. Levi was holding onto him by the armpit.

"Waa~" Eren started giggling uncontrolably, he was unsurprisingly very ticklish. Levi picked him up, secretly holding him as carefully as possible. Eren held onto Levi's shirt tightly while still giggling.

"Captain, we should probably get him a smaller outfit. Some food too" Petra stated, voice tainted with a bit of worry.

"Alright, Arlert, Ackermann, go to town and buy him some clothes. Braus, you'll be making him some food. Kirschtein and Springer will be joining you to make sure you don't eat the food." Levi ordered. Seconds later, the squad was ready and on their way.

"Captain, what can we do?" Historia asked, eager to help her classmate.

"You all can play with him while I prepare to give him a bath."

.

.

.

Levi carried Eren into his room and into his personal bathroom. Eren was amazed by how clean everything was, but when Eren thought about it, it was kind of expected of Levi.

He put Eren down on the tiled floor, careful not to let him fall on the ground.

"Cowpowal Wibai?" Eren asked looking up to Levi. 

Levi hummed to show that he was listening. He was never good with kids, but Eren seems to be behaving well enough.

"Bathe with me?" Eren rquested with very simple words, thanks to his lack of vocabulary.

Levi shook his head as a response. No way was he going to take a bath with a cadet, kid or not.

Eren visibly deflated at the response he was given. His mother would always take his baths with him, it always made bathtime a little more fun.

Levi felt a pang of guilt when he saw Eren's disappointment, but still, He definitely wasn't going to take a bath with him. He'll just help him wash up. 

He opened the tap to the tub and plugged up the water-drain. As soon as he deemed the water warm enough, he closed the tap and picked Eren up and into the water.

Slowly, Eren got more and more comfortable in the water.

"No splashing the water, Alright?" Levi asked, surprising Eren at how gentle he was being.

"Mhm!" Eren answered.

.

.

.

_Knock Knock Knock_

A few knocks were delivered to Levi's door.

"Captain, we've got Eren's clothes." came Armin's voice, muffled by the wood of the door.

"Come in and put it on the end of the bed." 

"Alright, Captain!" Armin went inside and did as he was told, and left to go join his friends in the Mess Hall. He did want to see Eren, but he knew he would see him later, besides he knew how much Eren loved his bathtime.

Levi finished bathing Eren and wiped him free from any excess water. When he was finished, he wrapped the towel around Eren's small body with it sagging a bit at the end. 'That wouldn't do.' Levi thought, he wasn't going to have his towel sag on the ground, no matter how clean his floor was. 

Eren started walking forward but was stopped by Levi's hand picking him up. "Uwaah~" Eren was carried across the bathroom and into Levi's bedroom.

Levi put Eren down on the bed and inspected the clothes Eren's friends had bought for him, there were three sets of clothes. One to wear during the day, one for the night and and extra pair of clothes along with a small jacket. Since Armin knew how Eren would always wear a jacket when they were together, he decided to buy one for him.

They also bought him a pair of short brown boots and scarf Levi guessed was bought by Mikasa.

Levi picked up the set of day clothes and brought the long sleeved shirt over Eren's head.

Eren held his arms up in order to help Levi with putting his shirt on. Right after, Levi brought the pants to his legs and put them on. Next, he gave Eren the jacket and let him put it on. Finally, Levi helped with putting Eren's boots on his feet.

Seconds after, he was finally finished with dressing Eren up.

.

.

.

 **End of Chapter Four**


	5. The Adventures of Tiny!Eren

**Summary for the Chapter:**

> Just some drabbles and shorts that happen to Eren and friends while the serum is still in-effect.

> **Memories**

"Well?" Levi questioned. He was waiting inside of Hange's office while they did some inspections on Eren.

"The serum will probably disappear from his system a few days from now." Hange explained.

"Probably?!" Exclaimed Levi. 

Completely ignoring Levi, Hange continued. "It seems like Eren still has vague memories of who everyone is, since he wasn't very scared of us. But it also looks like Eren still has the mindset and most of the memories of when he was a child."

"So what you're saying is that the memories of when he was a child and present Eren are mixing?"

Hange put her fingers on her chin and thought for a moment. "I guess you could say it's like that.." They shrugged.

.

.

.

> **Messy Eater**

Eren and Levi were on their way to the Mess Hall after they had done their daily inspection at Hange's. Eren didn't like how quiet Levi was being so he took it upon himself to start a conversation.

Of course, it wasn't a very understandable talk. Eren was just babbling non-stop, sometimes taking breaks to check if Levi was still paying attention.

Without Eren even noticing, they had already arrived at the Mess Hall. Eren finished any conversation he was having in favor of searching for his friends.

Levi had chuckled lowly to himself when he saw Eren stopped babbling to find his friends. He carried Eren to the table where his squad was seated, taking a seat in the spot that was saved at the front and placed Eren on his lap.

Sasha had made some stew for Eren since he couldn't eat solid foods. _Probably._

Eren picked up his spoon albeit a little clumsily since, well, he was a five year old.

He brought the spoon to his mouth and, surpise surprise, some of the soup fell, luckily, not on his new outfit. He tried several more times to actually feed himself before finally asking someone for help.

He grabbed a fistful of Levi's shirt and tugged a bit, enough to get his attention from whatever else he was doing. 

"Wibai! Wibai!" He whined and showed Levi the mess he had made while trying to feed himself in hopes that Levi would understand what he wanted.

Unfortunately, he didn't. Levi stared at Eren, confusion tainting his face.

"Eren probably wants you to feed him, Captain." Explained Petra she was always the most motherly of the group. Eren nodded his head furiously at Petra's explanation.

Levi stared off for a moment before finally saying. "Tch, messy brat." He took out his handkerchief from underneath his jacket and started wiping Eren's face. After his face was completly clean, free from any stew, Levi took the spoon Eren was holding out for him and carefully fed him the stew.

Needless to say, Eren was pretty content. Actually, he was quite happy.

.

.

.

> **Training Together**

Since Captain Levi was busy doing his paperwork that evening, Eren was instead joining his friends on their way to the training ground. 

He was gripping tightly onto Mikasa's shirt so he wouldn't get lost. Mikasa already asked Eren if he wanted her to carry him instead but he insisted that he wanted to walk. Although, Mikasa did constantly check on Eren to see if he was following.

A bit more walking later and they finally arrived at the training ground. Armin asked him if he wanted to join them and of course Eren said yes, even though he was definitely tired from all the walking. ' _The walk to the training ground was never this tiring when he was bigger._ ' he thought.

They all had to practice their combat that day so everyone had to pair up in their usual pairs and that meant Jean had to pair up with Eren.

"You better not hurt Eren." Mikasa ordered from her position in front of Armin. Jean only turned to look at her and nodded.

"Cw'mon Mika-cha. I can twake him!" Eren shouted towards Mikasa. Which was returned by a hum, a fond look in her eyes. Truth be told, Eren didn't know if he could actually take someone thrice his size, but he was determined to win against this horseface.

After a few moments, they started their combat training. Eren flew towards Jean, trying to land a punch on him but was avoided by Jean stepping to the side.

A few more punches later and Eren was sitting on top of Jean with his hands in the air, pride clearly written on his face, unaware that Jean had let him won.  
.  
.  
.

> **Help Me Clean!**

That afternoon Squad Levi was given the task of cleaning the storage room of the Survey Corps Headquarters.

Historia, Ymir and Armin had to sort out all the extra or broken equipment into some boxes. Mikasa, Sasha, Eld and Oluo had to sweep the ground. Petra, along with Eren had to clean the windows and windowsills and the rest were tasked with dusting the place.

Eren had tried to clean the windows but failed when he couldn't even reach them. Petra thought for a moment before walking towards one of the cupboards and pulling out a step-ladder for him.

Eren thanked Petra by giving her the biggest smile he could give and kissed her cheek. She started squealing but couldn't shake off the feeling of someone glaring at her from behind.

Eren tried to clean again, this time succesfully. He was cleaning when he realised he wouldn't be able to reach the top of the window. He also realised Petra couldn't reach the top as well.

Petra noticed that Eren stopped cleaning and looked to see Eren sticking his tongue out, clearly thinking about something.

"What's wrong, Eren?" She asked him, voice full of worry for the youngest member as of right now.

Eren continued thinking until he finally thought of something, making a little 'Aha!' sound.

"Up! Up!" exclaimed Eren, making grabby hands while looking up at Petra with that innocent look of his that no one could resist.

Petra hummed and picked Eren up, confusion clearly written on her face but didn't say anything about it. Eren put his hands up to the top of the window and finally Petra understood what he wanted.

.

.

.

> **Time To Sleep**

It was time to go to sleep and they decided that Eren would sleep with Levi, although with a bit of resistance from Mikasa, just in case something happened or the serum had any side affects.

Eren was going to be sleeping in his big shirt because Hange had told them that _Eren should be changing back tonight!_

Before they went to bed Eren had Levi help him get ready in the bathroom. Take off his clothes, bathe him, dry him and clothe him while also getting ready for bed himself. 

After he finished they went inside of the bedroom and walked towards the bed with Eren pulling a bit at Levi's pants to get him to move faster. 

Despite having done lots of things that day, Eren wasn't the slightest bit tired so before they went to bed, he let Eren play around his office a bit while he finished up his paperwork and reports.

.

.

.

After he finished all of the paperwork finally, he called someone to give them to Erwin.

Eren walked over to where he was standing at the door with tired eyes saying that he wanted to sleep while tugging at his pants weakly.

Chuckling slightly, Levi picked him up and brought him over to the bed where he carefully dropped him on top of the bed. He pulled the covers over Eren and tucked him in.

Just as he was about to leave, he felt a hand tugging at his shirt. He turned around to see Eren rubbing his eyes with one hand and the other holding onto him.

"Sleep with me?" Eren asked innocently. He knew how busy Levi usually was so he didn't want to keep him if he didn't want to, it's just his mom and dad would always sleep with him while holding onto him tightly.

Levi thought for a moment before remembering about the time Eren asked to bathe with him and how disappointed Eren looked so he agreed. He didn't want to have to see that look on Eren again.

Eren gave his thanks and smiled happily before snuggling into Levi's chest. Levi was stunned for a moment but hugged him back. After a few minutes they were sleeping peacefully in the warmth of each other.

.

.

.

**End of Chapter Five**


	6. I'm Back!

**Summary for the Chapter:**

> Eren is back to his normal self, but does he remember everything?

_'It's so fluffy.'_ Thought Eren.

 _'Wait. Where am I.'_ He thought again, last thing he remembered was being in Hange's office but this isn't Hange's office. It also definitely isn't his own bed down in the dungeon as it's much too soft.

Eren stirred a bit while trying to open his eyes. _Where was he?_ was the question that kept playing on his mind. Eventually though, his eyes fall open and he's met with the sight of very clean sheets. _'Definitely not my bed.'_ Eren stated in his mind. 

He rubbed his eyes, trying to get rid of the sleep tainting him. As soon as the drowsiness was no longer there, he realised he was inside of his superiors bedroom. Not just any superior though, Captain Levi's bedroom.

Something stirred from underneath him and he noticed he wasn't the only one sleeping on the bed. Captain Levi. The Captain Levi himself was sleeping beside him. 

Before Eren could react though, Levi stirred again and finally opened his eyes. Eren flinched and fell backwards.

"C-Captain l-Levi!? Oof!" Eren exclaimed and fell on his back off the side of the bed.

"Tch, noisy." Levi grumbled, voice raspy since he had just woken up. He crawled towards where Eren fell and helped him up onto the bed.

"W-what am I doing in y-your room, Corporal?" Eren asked, stuttering a little, but was determined to get an answer.

Levi looked at him for a moment, annoyance written on his face. "You don't remember?" Levi only asked him in turn.

Eren thought for a moment in case he remembered something. After a few seconds, he shook his head saying he couldn't remember anything after drinking something Hange gave him.

Levi pinched the bridge of his nose, he didn't want to explain everything, but he guessed it couldn't be helped.

.

.

.

Eren took a moment to process everything his captain told him before finally understanding everything.

"So, basically, I was a five year old for a couple of days and you and my friends took care of me?" Eren asked.

Levi simply nodded at his conclusion.

"..B-but.. what am I doing s-sleeping on your..bed?" Eren managed to stutter out the question on stuck on his mind since he woke up, albeit hesitantly.

Levi explained how he was the only one who could probably handle any side affects that happened, how Mikasa gave him to Levi threatening him that if he let anything happen to Eren she would cut off the thing in-between his legs.

Eren seemed pretty content with the answer but he was starting to feel a bit flustered sitting on top of Levi's bed.

"If that's all, I should probably get going now, Corporal." Levi nodded to him. 

He was in the middle of getting out of bed when he realised.

"Uh, Captain?" He called his captain which was earned by a nod and hum from the corporal showing he was indeed listening. "..Why am I not...wearing any pants?"

.

.

.

**End of Kid Yeager**

> _**Thank you for reading!** _

**Author's Note:**

> Thank you for reading!
> 
> If you have any suggestions for what Eren should turn into next, please comment down below. Although I won't be able to write until I actually finish this one..
> 
> Anyway, happy day!


End file.
